CHAPTER XLVI. 
HETEROSPORY AND THE SEED-HABIT. 
THE theme of this book has been the origin of a Land-Flora, not the 
examination of its ultimate developments: and accordingly the detailed 
study has related to the homosporous Archegoniatae, with only occasional 
allusion to those which are heterosporous, and hardly any to the Seed- 
bearing Plants. The reason for this lies in the high degree of certainty 
that the homosporous state was the pre-existent, and the heterosporous 
the derivative condition from it: any study of origins will therefore relate 
primarily to the former. But the upward evolution of Vascular Plants has 
been intimately connected with the differentiation of the spores according 
to sex, and the establishment of the Seed-Habit, changes which have 
brought with them biological advantages conducing to increased precision 
in the establishment of new individuals. The earlier step was the 
introduction of heterospory, which results only in minor reflex effects on 
the parent: the later adoption of the Seed-Habit has in certain cases 
been followed by a profound modification not only of the immediate 
spore-producing members themselves, but also of the parts which bear 
them. It will be necessary then to compare the condition of homosporous, 
heterosporous, and Seed-Bearing’ Plants, especially with respect to questions 
of amplification and reduction, such as have been treated of in Chapter XIX. 
It was there concluded (p. 241) that the production of the largest number 
of effective germs was the end of all development of the sporophyte: that 
any increase in their number involves amplification not only of the 
propagative system but also of thé nutritive: and consequently, other 
things being equal, there is a probability that homosporous plants as a 
whole should illustrate lines of amplification rather than lines of reduction. 
While admitting that reduction may occur in homosporous forms, the 
homosporous types have for the most part been recognised as constituting 
natural series of ascending complexity. 
The innovation of heterospory does not appear to have brought with 
it any general reduction of parts, but changes rather of the contents 
